The cellular protease inhibitor protease-nexin (PN) will be purified from human placental tissue or from cultures of human cells. The purified material will be used to define the role of PN as an inhibitor of plasminogen activators and other serine proteases of normal and malignant cells. We will identify and measure the concentrations of free serine proteases, free PN and protease-PN complexes in medium from these cultures. We will learn whether the well-documented elevated release of active proteases by malignant cells is caused by excess cellular release of proteases, insufficient cellular release of PN, or caused by abnormal properties of their PN or proteases. We will examine the ability of PN produced by normal cells to complex proteases released by malignant cells. We will establish how cellular release of PN is regulated when cellular expression of serine proteases is modulated by glucocorticoids, growth factors and tumor promotors. We will attempt to define the function(s) of the receptor-mediated binding and internalization of protease-PN complexes by normal human cells. It will be determined whether this process plays a role in protease-mediated stimulation of cell division by proteases, or in the control of cellular release of PN. The possibility that the cells bind and internalize free (active) PN will also be addressed. If this occurs it will be learned whether this plays a role in regulation of PN release, cellular accumulation and storage of PN, or protection of the cell surface from extracellular proteolysis. Finally, it will be determined if binding of protease-PN and free PN also occurs and functions similarly to malignant cells.